Defining the taxonomic status of Streptococcus suis serotype 33: the proposal for Streptococcus ruminantium sp. nov

Characterization of neurologic disease-associated Streptococcus suis strains within the United States swine herd and use of diagnostic tools

Streptococcus suis negatively impacts swine health, posing diagnostic and preventative challenges. S. suis can induce disease and also quietly reside on mucosal surfaces. The limited use of diagnostic tools to identify disease-associated strains and rule out differential diagnoses, alongside the complex ecology of S. suis, poses significant challenges in comprehending this important pathogen and defining pathotypes. This study evaluated 2,379 S. suis central nervous system (CNS) isolates from diagnostic submissions between 2015 and 2019. Isolates originating from submissions with histologic evidence of CNS infection (n = 1,032) were further characterized by standard and advanced diagnostic techniques. We identified 29 S. suis serotypes and 4 reclassified serotypes as putative causes of CNS disease. Among these, serotypes 1 and 7 emerged as the predominant putative causes of CNS infection (32% of submissions). Furthermore, 51 sequence types (STs), of which 15 were novel, were detected with ST1 predominating. Through whole-genome sequencing of 145 isolates, we observed that five commonly used virulence-associated genes (VAGs; epf, mrp, sly, ofs, and srtF) were not present in most disease-associated isolates, and matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) yielded false-positive results in 7% of isolates. These data indicate that (i) clinical signs and site of isolation alone are insufficient for defining a pathotype, (ii) S. suis serotypes and STs associated with CNS infection are more diverse than previously reported, (iii) MALDI-TOF MS may need to be supplemented with additional diagnostic tools for precise S. suis identification, and (iv) VAGs remain an unreliable means for identifying isolates associated with CNS disease.IMPORTANCEStreptococcus suis is an important and complex systemic bacterial pathogen of swine. Characterization of S. suis strains originating from pigs with histologic confirmation of neurologic disease is limited. Review of swine diagnostic submissions revealed that fewer than half of cases from which S. suis was isolated from the brain had histologic evidence of neurologic disease. This finding demonstrates that clinical signs and site of isolation alone are not sufficient for identifying a neurologic disease-associated strain. Characterization of strains originating from cases with evidence of disease using classic and advanced diagnostic techniques revealed that neurologic disease-associated strains are diverse and commonly lack genes previously associated with virulence.

Streptococcus suis subsp. hashimotonensis subsp. nov.: Lancefield group A antigen-positive organisms isolated from human clinical specimens and wild boar oral cavity samples

Three Streptococcus suis-like strains positive for Lancefield antigen group A were isolated from human boar bite wounds and the oral cavities of boars in Hashimoto City, Wakayama Prefecture, Japan, and their taxonomic positions were investigated. Application of the VITEK2 system identified all three isolates as S. suis with > 94 % probability. The isolates were assigned to S. suis based on the results of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) analysis (Biotyper score of 2.382) but were differentiated according to the characteristic signal peaks (4709 m/z and 9420 m/z) that were not present for S. suis. Sequence analysis of the 16S rRNA and sodA genes determined that the isolates were similar to S. suis; however, these genes appeared on a phylogenetic sub-branch. Phylogenetic analysis of the whole chromosomal DNA showed that the isolate formed a cluster with S. suis but with clear divergence. The average nucleotide index using BLAST between the clinical isolate (PAGU 2482) and a closely related reference strain of S. suis was 94.75 %, which was not clearly conclusive; however, digital DNA-DNA hybridization showed a value of 61.2 %. Biochemical reactions, including those with acid phosphatase, α-chymotrypsin, and tagatose (acidification), distinguished our isolates from S. suis. Thus, based on phylogenetic, genomic, and phenotypic characteristics and MALDI-TOF-MS signal patterns, we propose that the isolate with Lancefield group A positive characteristics be designated as a novel subspecies, Streptococcus suis subsp. hashimotonensis subsp. nov., with the type strain PAGU 2482T (GTC 18290T = CCUG 77434T).

Identification of plasminogen-binding sites in Streptococcus suis enolase that contribute to bacterial translocation across the blood-brain barrier

Streptococcus suis is an emerging zoonotic pathogen that can cause invasive disease commonly associated with meningitis in pigs and humans. To cause meningitis, S. suis must cross the blood-brain barrier (BBB) comprising blood vessels that vascularize the central nervous system (CNS). The BBB is highly selective due to interactions with other cell types in the brain and the composition of the extracellular matrix (ECM). Purified streptococcal surface enolase, an essential enzyme participating in glycolysis, can bind human plasminogen (Plg) and plasmin (Pln). Plg has been proposed to increase bacterial traversal across the BBB via conversion to Pln, a protease which cleaves host proteins in the ECM and monocyte chemoattractant protein 1 (MCP1) to disrupt tight junctions. The essentiality of enolase has made it challenging to unequivocally demonstrate its role in binding Plg/Pln on the bacterial surface and confirm its predicted role in facilitating translocation of the BBB. Here, we report on the CRISPR/Cas9 engineering of S. suis enolase mutants eno261, eno252/253/255, eno252/261, and eno434/435 possessing amino acid substitutions at in silico predicted binding sites for Plg. As expected, amino acid substitutions in the predicted Plg binding sites reduced Plg and Pln binding to S. suis but did not affect bacterial growth in vitro compared to the wild-type strain. The binding of Plg to wild-type S. suis enhanced translocation across the human cerebral microvascular endothelial cell line hCMEC/D3 but not for the eno mutant strains tested. To our knowledge, this is the first study where predicted Plg-binding sites of enolase have been mutated to show altered Plg and Pln binding to the surface of S. suis and attenuation of translocation across an endothelial cell monolayer in vitro.

Streptococcus ruminantium-associated sheep mastitis outbreak detected in Italy is distinct from bovine isolates

Streptococcus ruminantium is the causative agent of several bovine and ovine diseases, however reports are uncommon and application of whole genome sequencing to identify is rare. We report for the first time, a severe ovine mastitis outbreak caused by S. ruminantium in Italy, 2022. S. ruminantium was isolated from 12 adult lactating ewes with diffuse nodules in the mammary parenchyma and predominantly serous and clotted milk. All outbreak isolates, along with five additional historical Italian isolates (between 2011 and 2017), were genomically characterised and then analysed in the context of all publicly available S. ruminantium genomes. Antimicrobial susceptibility testing was performed to determine the MICs of 16 antibiotics. The results showed that all isolates were susceptible to all antimicrobials tested except kanamycin. Single Nucleotide Variant analysis confirmed this as a clonal outbreak across 10 sheep (≤ 15 SNVs), while the two others were colonised by more distantly related clones (≤ 53 pairwise SNVs), indicating the presence of multiple infecting lineages. The five historical S. ruminantium isolates were comprised of genetically-distant singletons (between 1259 and 5430 pairwise SNVs to 2022 outbreak isolates). Ovine isolates were found to be genetically distinct to bovine isolates, forming monophyletic groups. Bovine isolates were similarly made up of singleton clones in all but two isolates. Taken together, our genomic analysis using all globally available genomes is consistent with general opportunistic pathogenesis of S. ruminantium. We encourage future genomic surveillance efforts to facilitate outbreak detection, as well as improve our understanding of this poorly-understood, multi-host, zoonotic pathogen.

Rapid Diagnostic of Streptococcus suis in Necropsy Samples of Pigs by thrA-Based Loop-Mediated Isothermal Amplification Assay

Streptococcus (S.) suis presents a serious threat to the pig industry as well as food safety and public health. Although several LAMP assays have been developed for the identification of S. suis, no universal assay is so far available for the field-suitable examination of clinical pig specimens. Based on the thrA housekeeping gene, a new loop-mediated isothermal amplification (LAMP) assay was developed and validated for the detection of S. suis in the brain and joints of pigs. For this LAMP assay, two different methods for the extraction of DNA from brain and joint swabs were compared. Using the LPTV boiling method, the detection limit of LAMP was 1.08 CFU/reaction, while the detection limit was 53.8 CFU/reaction using a commercial DNA extraction kit. The detection limits of thrA-LAMP in combination with the LPTV boiling method were 104-105 CFU/swab in the presence of brain tissue and 103-104 CFU/swab in the presence of joint tissue. The diagnostic quality criteria of LAMP were determined by the examination of 49 brain swabs and 34 joint swabs obtained during routine diagnostic necropsies. Applying the LPTV boiling method to brain swabs, the sensitivity, specificity, and positive and negative predictive values of thrA-LAMP were 88.0, 95.8, 95.7, and 88.5% using cultural investigation as a reference method, and 76.7, 100, 100, and 73.1% using real-time PCR as a reference method. Based on these results, the thrA-LAMP assay combined with the LPTV boiling method is suitable for rapid detection of S. suis from brain swabs.

Streptococcus oriscaviae sp. nov. Infection Associated with Guinea Pigs

Pet bite-related infections are commonly caused by the pet's oral flora transmitted to the animal handlers through the bite wounds. In this study, we isolated a streptococcus, HKU75T, in pure culture from the purulent discharge collected from a guinea pig bite wound in a previously healthy young patient. HKU75T was alpha-hemolytic on sheep blood agar and agglutinated with Lancefield group D and group G antisera. API 20 STREP showed that the most likely identity for HKU75T was S. suis I with 85.4% confidence while Vitek 2 showed that HKU75T was unidentifiable. MALDI-TOF MS identified HKU75T as Streptococcus suis (score of 1.86 only). 16S rRNA gene sequencing showed that HKU75T was most closely related to S. parasuis (98.3% nucleotide identity), whereas partial groEL and rpoB gene sequencing showed that it was most closely related to S. suis (81.8% and 89.8% nucleotide identity respectively). Whole genome sequencing and intergenomic distance determined by ANI revealed that there was <85% identity between the genome of HKU75T and those of all other known Streptococcus species. Genome classification using concatenated sequences of 92 bacterial core genes showed that HKU75T belonged to the Suis group. groEL gene sequences identical to that of HKU75T could be directly amplified from the oral cavities of the two guinea pigs owned by the patient. HKU75T is a novel Streptococcus species, which we propose to be named S. oriscaviae. The oral cavity of guinea pigs is presumably a reservoir of S. oriscaviae. Some of the reported S. suis strains isolated from clinical specimens may be S. oriscaviae. IMPORTANCE We reported the discovery of a novel Streptococcus species, propose to be named Streptococcus oriscaviae, from the pus collected from a guinea pig bite wound in a healthy young patient. The bacterium was initially misidentified as S. suis/S. parasuis by biochemical tests, mass spectrometry. and housekeeping genes sequencing. Its novelty was confirmed by whole genome sequencing. Comparative genomic studies showed that S. oriscaviae belongs to the Suis group. S. oriscaviae sequences were detected in the oral cavities of the two guinea pigs owned by the patient, suggesting that the oral cavity of guinea pigs could be a reservoir of S. oriscaviae. Some of the reported S. suis strains may be S. oriscaviae. Further studies are warranted to refine our knowledge on this novel Streptococcus species.

Complete Genome Sequences of Three Streptococcus ruminantium Strains Obtained from Endocarditis Lesions of Cattle in Japan

Streptococcus ruminantium is a close relative of Streptococcus suis, an important zoonotic pathogen that causes various diseases in pigs and humans. Here, we report the complete genome sequences of three S. ruminantium strains isolated from bovine endocarditis in Japan.

First Report of Streptococcus ruminantium in Wildlife: Phenotypic Differences with a Spanish Domestic Ruminant Isolate

Streptococcus ruminantium is a recent reclassification of the former Streptococcus suis serovar 33. Although knowledge about S. suis is extensive, information on S. ruminantium host range and pathogenic potential is still scarce. This bacterium has been isolated from lesions in domestic ruminants, but there are no reports in wild animals. Here, we provide information on lesions associated with S. ruminantium in Pyrenean chamois (Rupicapra pyrenaica) and domestic sheep from NE Spain, as well as phenotypic biopatterns and antimicrobial resistance (AMR) of the isolates. Overall, lesions caused by S. ruminantium were similar to those caused by S. suis, excluding polyserositis. Heterogeneity of the phenotypic profiles was observed within the S. ruminantium strains by VITEK-2, resulting in only two tests common to all S. ruminantium isolates and different from S. suis: Alpha-Galactosidase and Methyl-B-D-Glucopyranoside, both positive for S. suis and negative for S. ruminantium strains. Isolates from Pyrenean chamois were susceptible to all antimicrobials tested, except danofloxacin, whereas the domestic sheep isolate was resistant to tetracycline. In conclusion, S. ruminantium can cause infection and be associated with pathology in both wild and domestic ruminants. Due to its phenotypic diversity, a specific PCR is optimal for identification in routine diagnosis.

Whole-Genome Sequencing Evaluation of MALDI-TOF MS as a Species Identification Tool for Streptococcus suis

Streptococcus suis is an important bacterial pathogen in pigs that may also cause zoonotic disease in humans. The aim of the study was to evaluate matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) identification of S. suis case isolates from diseased pigs and tonsil isolates from healthy pigs and wild boar using sequence analysis methods. Isolates (n = 348) that had been classified as S. suis by MALDI-TOF MS were whole-genome sequenced and investigated using analyses of (i) the 16S rRNA gene, (ii) the recN gene, and (iii) whole-genome average nucleotide identity (ANI). Analysis of the 16S rRNA gene indicated that 82.8% (288 out of 348) of the isolates were S. suis, while recN gene analysis indicated that 75.6% (263 out of 348) were S. suis. ANI analysis classified 44.3% (154 out of 348) as S. suis. In total, 44% (153 out of 348) of the investigated isolates were classified as S. suis by all of the species identification methods employed. The mean MALDI-TOF MS score was significantly higher for the S. suis case isolates than for the tonsil isolates; however, the difference is of limited practical use. The results show that species confirmation beyond MALDI-TOF MS is needed for S. suis isolates. Since the resolution of 16S rRNA gene analysis is too low for Streptococcus spp., ANI analysis with a slightly lowered cutoff of 94% may be used instead of, or in addition to, recN gene analysis. Supplementation of the MALDI-TOF MS reference library with mass spectra from S. orisratti, S. parasuis, S. ruminantium, and additional S. suis serotypes should be considered in order to produce more accurate classifications.

Effective Antibacterial and Antihemolysin Activities of Ellipticine Hydrochloride against Streptococcus suis in a Mouse Model

Streptococcal toxic shock-like syndrome (STSLS) caused by the epidemic strain of Streptococcus suis leads to severe inflammation and high mortality. The life and health of humans and animals are also threatened by the increasingly severe antimicrobial resistance in Streptococcus suis There is an urgent need to discover novel strategies for the treatment of S. suis infection. Suilysin (SLY) is considered to be an important virulence factor in the pathogenesis of S. suis In this study, ellipticine hydrochloride (EH) was reported as a compound that antagonizes the hemolytic activity of SLY. In vitro, EH was found to effectively inhibit SLY-mediated hemolytic activity. Furthermore, EH had a strong affinity for SLY, thereby directly binding to SLY to interfere with the hemolytic activity. Meanwhile, it was worth noting that EH was also found to have a significant antibacterial activity. In vivo, compared with traditional ampicillin, EH not only significantly improved the survival rate of mice infected with S. suis 2 strain Sc19 but also relieved lung pathological damage. Furthermore, EH effectively decreased the levels of inflammatory cytokines (interleukin-6 [IL-6], tumor necrosis factor alpha [TNF-α]) and blood biochemistry enzymes (alanine transaminase [ALT], aspartate transaminase [AST], creatine kinase [CK]) in Sc19-infected mice. Additionally, EH markedly reduced the bacterial load of tissues in Sc19-infected mice. In conclusion, our findings suggest that EH can be a potential compound for treating S. suis infection in view of its antibacterial and antihemolysin activity.IMPORTANCE In recent years, the inappropriate use of antibiotics has unnecessarily caused the continuous emergence of resistant bacteria. The antimicrobial resistance of Streptococcus suis has also become an increasingly serious problem. Targeting virulence can reduce the selective pressure of bacteria on antibiotics, thereby alleviating the development of bacterial resistance to a certain extent. Meanwhile, the excessive inflammatory response caused by S. suis infection is considered the primary cause of acute death. Here, we found that ellipticine hydrochloride (EH) exhibited effective antibacterial and antihemolysin activities against S. suisin vitroIn vivo, compared with ampicillin, EH had a significant protective effect on S. suis serotype 2 strain Sc19-infected mice. Our results indicated that EH, with dual antibacterial and antivirulence effects, will contribute to treating S. suis infections and alleviating the antimicrobial resistance of S. suis to a certain extent. More importantly, EH may develop into a promising drug for the prevention of acute death caused by excessive inflammation.

Rapid Detection of mrp, epf, and sly Genes by Loop-Mediated Isothermal Amplification in Streptococcus suis

Streptococcus suis remains a serious threat to the worldwide swine industry and human health. In this study, rapid assays for the detection of three common virulence-related factors (mrp, epf, and sly) were developed, evaluated, and applied. Loop-mediated isothermal amplification (LAMP) primers were designed using Primer Explorer V5 software. The sensitivity and specificity of the LAMP assays were determined based on sample turbidity. For all three genes, LAMP assays were performed at 62°C with a reaction time of 60 min. The detection limit of conventional polymerase chain reaction (PCR) was 1 ng/μL, 10 pg/μL, and 100 fg/μL for the epf, sly, and mrp genes, respectively. For the LAMP assays, the detection limits were 10 pg/μL, 10 fg/μL, and 100 fg/μL for epf, sly, and mrp, respectively, representing sensitivities 100-1000 times higher than those of the PCR assay. Furthermore, when the LAMP assays were applied to clinical strains, the results were consistent with those of the PCR assay, confirming the LAMP assays as rapid and reliable detection techniques. In conclusion, the LAMP assays described in this study have the potential to become standard methods to detect the virulence factors mrp, epf, and sly. To the best of our knowledge, this is the first study to report the application of LAMP to detect the mrp, epf, and sly genes.

Involvement of Various Enzymes in the Physiology and Pathogenesis of Streptococcus suis

Streptococcus suis causes severe infections in both swine and humans, making it a serious threat to the swine industry and public health. Insight into the physiology and pathogenesis of S. suis undoubtedly contributes to the control of its infection. During the infection process, a wide variety of virulence factors enable S. suis to colonize, invade, and spread in the host, thus causing localized infections and/or systemic diseases. Enzymes catalyze almost all aspects of metabolism in living organisms. Numerous enzymes have been characterized in extensive detail in S. suis, and have shown to be involved in the pathogenesis and/or physiology of this pathogen. In this review, we describe the progress in the study of some representative enzymes in S. suis, such as ATPases, immunoglobulin-degrading enzymes, and eukaryote-like serine/threonine kinase and phosphatase, and we highlight the important role of various enzymes in the physiology and pathogenesis of this pathogen. The controversies about the current understanding of certain enzymes are also discussed here. Additionally, we provide suggestions about future directions in the study of enzymes in S. suis.

Streptococcus suis in Swedish grower pigs: occurrence, serotypes, and antimicrobial susceptibility

BACKGROUND

Streptococcus suis is a major cause of meningitis, arthritis, and pneumonia in pigs worldwide, and an emerging pathogen in humans. In Sweden, S. suis has previously received little attention but has in recent years become increasingly recognized as affecting the pig production. The aim of the present study was to investigate the occurrence, serotypes and antimicrobial susceptibility of S. suis in Swedish grower pigs from herds with and without reported S. suis associated disease, as well as possible associations between S. suis associated disease and selected environmental and production factors. Swab samples were taken from the tonsils of clinically healthy 8-13-week-old grower pigs from ten case herds and ten control herds. Isolates were cultured, identified using MALDI-TOF MS, and serotyped using latex agglutination. The antimicrobial susceptibility of 188 isolates was tested using broth microdilution. Production data was gathered and environmental parameters were measured on the farms.

RESULTS

Streptococcus suis was isolated from 95% of the sampled pigs in both the case and the control herds. Serotypes 3, 4, 5, 7, 9, 10, 11, 15, 16, and 17-34 were detected, although a majority of the isolates (81.5%) were non-typeable. There was less diversity among the serotypes isolated from the case herds than among those from the control herds; four and nine different serotypes, respectively. Isolates resistant to penicillin (3.8%) were reported for the first time in Sweden. Tetracycline resistance was common (88.4%). No association was noted between the production and the environmental factors investigated, and the carriership of S. suis.

CONCLUSIONS

The carriership of S. suis was found to be higher in clinically healthy Swedish pigs than previously estimated, and for the first time, the presence of Swedish isolates resistant to penicillin was reported. Many of the most commonly disease-associated serotypes, e.g. serotypes 2, 9, 3, and 7, were detected in healthy grower pigs although further studies are needed to investigate the virulence of these isolates.

Capsular serotypes, antimicrobial susceptibility, and the presence of transferable oxazolidinone resistance genes in Streptococcus suis isolated from healthy pigs in China

Streptococcus suis is a pig pathogen and a vector of zoonotic diseases that can cause severe systemic infection in humans. S. suis can colonize the nasal cavity, tonsils, and upper respiratory, genital, and digestive tracts in healthy pigs. Here, to determine prevalence, serotype distribution, and antimicrobial susceptibility of S. suis in healthy pigs, we collected 1813 nasal cavity samples from healthy pigs raised on 17 independent farms in six Chinese provinces between 2016 and 2018. We obtained 223 S. suis isolates (12.3 %) and the antimicrobial susceptibility to a panel of 11 antimicrobial agents was measured by microbroth dilution. Most S. suis isolates (98.7 %) were resistant to at least three classes of antimicrobial agents. The optrA gene conferring resistance to oxazolidinones and phenicols was identified in the chromosome of 27 isolates and on a ∼40-kb plasmid in one isolate; to the best of our knowledge, this was the first report of plasmid-borne optrA gene in S. suis. The genetic environment of optrA showed substantial diversity and could be divided into eleven different types. Interestingly, some fragments of the 89 K pathogenicity island (PAI) were observed together with optrA in 3 isolates, which warrants further attention. Capsular serotypes of S. suis isolates were determined by multiplex PCR. Serotype 29 was the most prevalent, followed by serotype 7 and serotype 2. The presence of highly virulent serotype 2 strains may pose a threat to public health.

Development of a mismatch amplification mutation assay to correctly serotype isolates of Streptococcus suis serotypes 1, 2, 1/2, and 14

Streptococcus suis is one of the most important bacterial swine pathogens worldwide and is an emerging pathogen in humans. There are 29 serotypes, and serotyping, which is based on the antigenicity of the capsular polysaccharide (CPS) or on its coding genes, is often part of routine identification and provides further information regarding S. suis virulence and zoonotic potential. Serotypes 2 and 14 possess high zoonotic potential, and serotype 1/2 is the serotype most frequently isolated from diseased pigs in North America. PCR has replaced antibody-based techniques to perform serotyping. However, traditional PCR is not able to differentiate serotype 2 from 1/2 and serotype 1 from 14, given that the only difference in the cps loci of those serotype pairs is a nonsynonymous single-nucleotide polymorphism. We developed a mismatch amplification mutation assay (MAMA)-PCR that was able to correctly serotype 148 isolates previously known to be serotypes 1, 2, 1/2, or 14. This technique will be highly useful in animal and human health laboratories performing PCR serotyping of S. suis isolates.

Tools for Molecular Epidemiology of Streptococcus suis

Diseases caused by Streptococcus suis are a significant economic and welfare concern in pigs as well as in humans. Several molecular methods have been applied to investigate S. suis strain diversity and identify phylogenetic groups. Multilocus sequence typing (MLST), commonly used to differentiate between S. suis strains, has been instrumental in identifying that the species is genetically highly diverse. Recent advances in whole-genome analysis have resulted in schemes permitting the classification of S. suis populations as pathogenic or non-pathogenic, or disease-associated or non-disease associated. Here, we review these and other molecular approaches that can be used for surveillance, outbreak tracking, preventative health management, effective treatment and control, as well as vaccine development, including PCR based-assays that are easy to apply in modest diagnostic settings and which allow for the rapid screening of a large number of isolates at relatively low cost, granting the identification of several major clonal complexes of the S. suis population.

PmtA functions as a ferrous iron and cobalt efflux pump in Streptococcus suis

Transition metals are nutrients essential for life. However, an excess of metals can be toxic to cells, and host-imposed metal toxicity is an important mechanism for controlling bacterial infection. Accordingly, bacteria have evolved metal efflux systems to maintain metal homeostasis. Here, we established that PmtA functions as a ferrous iron [Fe(II)] and cobalt [Co(II)] efflux pump in Streptococcus suis, an emerging zoonotic pathogen responsible for severe infections in both humans and pigs. pmtA expression is induced by Fe(II), Co(II), and nickel [Ni(II)], whereas PmtA protects S. suis against Fe(II) and ferric iron [Fe(III)]-induced bactericidal effect, as well as Co(II) and zinc [Zn(II)]-induced bacteriostatic effect. In the presence of elevated concentrations of Fe(II) and Co(II), ΔpmtA accumulates high levels of intracellular iron and cobalt, respectively. ΔpmtA is also more sensitive to streptonigrin, a Fe(II)-activated antibiotic. Furthermore, growth defects of ΔpmtA under Fe(II) or Co(II) excess conditions can be alleviated by manganese [Mn(II)] supplementation. Finally, PmtA plays a role in tolerance to H₂O₂-induced oxidative stress, yet is not involved in the virulence of S. suis in mice. Together, these data demonstrate that S. suis PmtA acts as a Fe(II) and Co(II) efflux pump, and contributes to oxidative stress resistance.

Analysis of Porcine Pro- and Anti-Inflammatory Cytokine Induction by S. suis In Vivo and In Vitro

Weaning piglets are susceptible to the invasive Streptococcus (S.) suis infection, which can result in septicemia. The aim of this study was to investigate the cytokine profile induced upon S. suis infection of blood, to determine the cellular sources of those cytokines, and to study the potential effects of the induced cytokines on bacterial killing. We measured TNF-α, IL-6, IFN-γ, IL-17A and IL-10 after an experimental intravenous infection with S. suis serotype 2 in vivo, and analyzed whole blood, peripheral blood mononuclear cells (PBMC) and separated leukocytes to identify the cytokine-producing cell type(s). In addition, we used a reconstituted whole blood assay to investigate the effect of TNF-α on bacterial killing in the presence of different S. suis-specific IgG levels. An increase in IL-6 and IL-10, but not in IFN-γ or IL-17A, was observed in two of three piglets with pronounced bacteremia 16 to 20 h after infection, but not in piglets with controlled bacteremia. Our results confirmed previous findings that S. suis induces TNF-α and IL-6 and could demonstrate that TNF-α is produced by monocytes in vitro. We further found that IL-10 induction resulted in reduced secretion of TNF-α and IL-6. Rapid induction of TNF-α was, however, not crucial for in vitro bacterial killing, not even in the absence of specific IgG.

From Stable to Lab-Investigating Key Factors for Sudden Deaths Caused by Streptococcus suis

Swine stocks are endemically infected with the major porcine pathogen Streptococcus (S.) suis. The factors governing the transition from colonizing S. suis residing in the tonsils and the exacerbation of disease have not yet been elucidated. We analyzed the sudden death of fattening pigs kept under extensive husbandry conditions in a zoo. The animals died suddenly of septic shock and showed disseminated intravascular coagulopathy. Genotypic and phenotypic characterizations of the isolated S. suis strains, a tonsillar isolate and an invasive cps type 2 strain, were conducted. Isolated S. suis from dead pigs belonged to cps type 2 strain ST28, whereas one tonsillar S. suis isolate harvested from a healthy animal belonged to ST1173. Neither S. suis growth, induction of neutrophil extracellular traps, nor survival in blood could explain the sudden deaths. Reconstituted blood assays with serum samples from pigs of different age groups from the zoo stock suggested varying protection of individuals against pathogenic cps type 2 strains especially in younger pigs. These findings highlight the benefit of further characterization of the causative strains in each case by sequence typing before autologous vaccine candidate selection.

Genotypic diversity of Streptococcus suis and the S. suis-like bacterium Streptococcus ruminantium in ruminants

Although Streptococcus suis has attracted public attention as a major swine and human pathogen, this bacterium has also been isolated from other animals, including ruminants. However, recent taxonomic studies revealed the existence of other species that were previously identified as S. suis, and some of these isolates were reclassified as the novel species Streptococcus ruminantium. In Japan, biochemically identified S. suis is frequently isolated from diseased ruminants; however, such isolates have not yet been identified accurately, and their aetiological importance in ruminants is unclear. Therefore, to understand the importance of S. suis and S. suis-like bacteria in ruminants, we reclassified S. suis isolates from ruminants according to the updated classification and investigated their genetic diversity. Although both S. suis and S. ruminantium were isolated from healthy and diseased ruminants, most of the isolates from diseased animals were S. ruminantium, implying that S. ruminantium is more likely to be associated with ruminant disease than S. suis. However, the ruminant S. suis and S. ruminantium isolates from diseased animals were classified into diverse genotypes rather than belonging to certain clonal groups. Genome sequence analysis of 20 S. ruminantium isolates provided information about the antibiotic resistance, potential virulence, and serological diversity of this species. We further developed an S. ruminantium-specific PCR assay to aid in the identification of this bacterium. The information obtained and the method established in this study will contribute to the accurate diagnosis of ruminant streptococcal infections.

Serotype and Genotype (Multilocus Sequence Type) of Streptococcus suis Isolates from the United States Serve as Predictors of Pathotype

Streptococcus suis is a significant cause of mortality in piglets and growing pigs worldwide. The species contains pathogenic and commensal strains, with pathogenic strains causing meningitis, arthritis, endocarditis, polyserositis, and septicemia. Serotyping and multilocus sequence typing (MLST) are primary methods to differentiate strains, but the information is limited for strains found in the United States.

Streptococcus suis is a significant cause of mortality in piglets and growing pigs worldwide. The species contains pathogenic and commensal strains, with pathogenic strains causing meningitis, arthritis, endocarditis, polyserositis, and septicemia. Serotyping and multilocus sequence typing (MLST) are primary methods to differentiate strains, but the information is limited for strains found in the United States. The objective of this study was to characterize the diversity of 208 S. suis isolates collected between 2014 and 2017 across North America (mainly the United States) by serotyping and MLST and to investigate associations between subtype and pathotype classifications (pathogenic, possibly opportunistic, and commensal), based on clinical information and site of isolation. Twenty serotypes were identified, and the predominant serotypes were 1/2 and 7. Fifty-eight sequence types (STs) were identified, and the predominant ST was ST28. Associations among serotypes, STs, and pathotypes were investigated using odds ratio and clustering analyses. Evaluation of serotype and ST with pathotype identified a majority of isolates of serotypes 1, 1/2, 2, 7, 14, and 23 and ST1, ST13, ST25, ST28, ST29, ST94, ST108, ST117, ST225, ST373, ST961, and ST977 as associated with the pathogenic pathotype. Serotypes 21 and 31, ST750, and ST821 were associated with the commensal pathotype, which is composed of isolates from farms with no known history of S. suis-associated disease. Our study demonstrates the use of serotyping and MLST to differentiate pathogenic from commensal isolates and establish links between pathotype and subtype, thus increasing the knowledge about S. suis strains circulating in the United States.

CopA Protects Streptococcus suis against Copper Toxicity

Streptococcus suis is a zoonotic pathogen that causes great economic losses to the swine industry and severe threats to public health. A better understanding of its physiology would contribute to the control of its infections. Although copper is an essential micronutrient for life, it is toxic to cells when present in excessive amounts. Herein, we provide evidence that CopA is required for S. suis resistance to copper toxicity. Quantitative PCR analysis showed that copA expression was specifically induced by copper. Growth curve analyses and spot dilution assays showed that the ΔcopA mutant was defective in media supplemented with elevated concentrations of copper. Spot dilution assays also revealed that CopA protected S. suis against the copper-induced bactericidal effect. Using inductively coupled plasma-optical emission spectroscopy, we demonstrated that the role of CopA in copper resistance was mediated by copper efflux. Collectively, our data indicated that CopA protects S. suis against the copper-induced bactericidal effect via copper efflux.

Purpura fulminans with Lemierre's syndrome caused by Gemella bergeri and Eikenella corrodens: a case report

BACKGROUND

Gemella bergeri is one of the nine species of the genus Gemella and is relatively difficult to identify. We herein describe the first case of septic shock due to a Gemella bergeri coinfection with Eikenella corrodens.

CASE PRESENTATION

A 44-year-old Asian man with a medical history of IgG4-related ophthalmic disease who was prescribed corticosteroids (prednisolone) presented to our hospital with dyspnea. On arrival, he was in shock, and a purpuric eruption was noted on both legs. Contrast enhanced computed tomography showed fluid retention at the right maxillary sinus, left lung ground glass opacity, and bilateral lung irregular opacities without cavitation. Owing to suspected septic shock, fluid resuscitation and a high dose of vasopressors were started. In addition, meropenem, clindamycin, and vancomycin were administered. Repeat computed tomography confirmed left internal jugular and vertebral vein thrombosis. Following this, the patient was diagnosed with Lemierre's syndrome. Furthermore, he went into shock again on day 6 of hospitalization. Additional soft tissue infections were suspected; therefore, bilateral below the knee amputations were performed for source control. Cultures of the exudates from skin lesions and histopathological samples did not identify any pathogens, and histopathological findings showed arterial thrombosis; therefore it was concluded that the second time shock was associated with purpura fulminans. Following this, his general status improved. He was transferred to another hospital for rehabilitation. The blood culture isolates were identified as Gemella bergeri and Eikenella corrodens. Gemella bergeri was identified by matrix-assisted laser desorption ionization-time of flight mass spectrometry and confirmed by 16S rRNA gene sequencing later. The primary focus of the infection was thought to be in the right maxillary sinus, because the resolution of the fluid retention was confirmed by repeat computed tomography.

CONCLUSIONS

Gemella bergeri can be the causative pathogen of septic shock. If this pathogen cannot be identified manually or through commercial phenotypic methods, 16S rRNA gene sequencing should be considered.

Complete Genome Sequence of Streptococcus ruminantium sp. nov. GUT-187T (=DSM 104980T =JCM 31869T), the Type Strain of S. ruminantium, and Comparison with Genome Sequences of Streptococcus suis Strains

Streptococcus ruminantium sp. nov. of type strain GUT-187^T, previously classified as Streptococcus suis serotype 33, is a recently described novel streptococcal species. This study was designed to determine the complete genome sequence of S. ruminantium GUT-187^T using a combination of Oxford Nanopore and the Illumina platform, and to compare this sequence with the genomes of 27 S. suis representative strains. The genome of GUT-187^T was 2,090,539 bp in size, with a GC content of 40.01%. This genome contained 1,961 predicted protein coding DNA sequences (CDSs); of these, 1,685 (85.9%) showed similarity with S. suis CDSs. Of the remaining 276 CDSs, 81 (29.3%) showed some degree of similarity with CDSs of other streptococcal species. The genome of GUT-187^T contained no intact prophage. The numbers of prophages and CRISPR spacers, as well as the presence or absence of genes encoding CRISPR-associated proteins, differed in S. ruminantium and S. suis. A phylogenetic analysis indicates that GUT-187^T may be outgroup to the S. suis strains in our sample, thereby justifying its classification as distinct species. Gene mapping indicated 10.2 times of massive genome rearrangements in average occurred between S. ruminantium and S. suis. There was no significant statistical difference in clusters of orthologous group distribution between S. ruminantium and S. suis.

Bovine vegetative endocarditis caused by Streptococcus suis

A 5-month-old crossbred beef steer died after exhibiting astasia. A postmortem examination revealed verrucous endocarditis and numerous renal hemorrhages. Gram-positive bacteria were identified in the necrotic lesions of the verruca and mitral valve via histopathological analysis. Multifocal necrosis and hemorrhage were detected in the renal cortex. Gram-positive cocci isolated from the verruca were identified via biochemical tests and 16S rRNA gene sequence analysis as Streptococcus suis. Serotyping indicated that the S. suis isolates were untypable, following which these isolates were classified as a new sequence type (ST1000) via multi-locus sequence typing. S. suis is an important pathogen of pigs. However, clinical cases in cattle are rare. This report is intended to provide information that may be useful in the diagnosis of streptococcal disease in cattle.

Development of PCR for identifying Streptococcus parasuis, a close relative of Streptococcus suis

Streptococcus parasuis has recently been removed taxonomically from Streptococcus suis, a zoonotic pathogen. S. parasuis has been detected in healthy pigs and in diseased pigs, which suggests that S. parasuis is involved in the normal microbiota of pigs and has potential pathogenicity. However, the pathogenicity of S. parasuis in pigs is unclear because of the lack of appropriate detection methods that discriminate S. parasuis from S. suis. In this study, we developed a PCR method that is specific for S. parasuis. The detection limit of the PCR was 350 CFU per reaction. Bacteria isolated from the saliva of eight pigs were collected and examined by PCR. Sixty-four isolates positive for PCR were obtained from the samples of all pigs. Thirteen of the 64 isolates were genetically confirmed as S. parasuis, and biologically and biochemically had nearly the same features of known S. parasuis strains, which suggested that strains positive for PCR were S. parasuis. Among the 64 isolates, 28 isolates were serotypes 20, 22, or 26 in the S. suis serotyping scheme. The remaining 36 isolates were untypeable, which suggested the presence of novel serotypes or a capsule-negative form. Therefore, the PCR method described in this study is a useful tool for identifying S. parasuis, and can be used in etiological studies on this bacterium.